1. Field of the Invention
The present invention relates generally to belt drive systems and, more particularly, to a belt tensioner for a reversible pulley system.
2. Description of the Related Art
In many belt drive system applications, it is important to optimize belt tension. The purpose of a belt tensioner is to maintain a substantially constant tension in a drive belt. In most applications, the belt connects stationary pulleys. Hence, belt tension can be set by affixing one pulley to a mount having an adjustable linkage to a fixed mounting surface. Automobile engine belts are common examples of this type of system.
However, in other applications, a belt drive system may be used where the belt is used to position another device. For example, a computer may be used to provide drive signals to an ink-jet printer (a high-speed printing process in which thermally excited ink is broken up into electrostatically charged droplets which are controlled by a computer program into positions that form printed characters on a print media). An ink pen carriage is rapidly and repeatedly scanned back and forth across the print media by providing a belt drive device in which the pen carriage is positioned by "riding" the belt. Positioning of the printhead to the print media is, of course, critical to prevent a printing error. Hence, belt tension is an important feature. One example of such a prior art mechanism is shown in FIG. 1 (prior art).
A belt 100 connects a reversible motor 300 to an idler pulley 500. The pulley axle 700 fits slidingly in slots 900 in mounting frame 110. The belt 100 extends through an aperture 130 in frame 110. A pen carriage (not shown) could ride a guide bar 150 and be attached to the belt 100. Since the pulley axle 700 makes a sliding fit and the belt must be long enough to reach beyond end 170 of the mount 110 to encircle the pulley 500 before fit into slots 900, a tensioner 190 is used to achieve the proper tension. After the pulley 500 is fit into the slots 900, the tensioner 190 is inserted such that the axle 700 will ride on tensioner surface 210. Extension tab 230, with tensioning spring 250 surrounding it, is rotatingly slipped into slot 270 of the mount 110. By designing to a close tolerance, the tensioner surface 210 will pull the pulley outward along the slots 900 just until the belt 100 is properly tensioned.
One concern is to maintain tension in the belt over a wide rage of tolerances in the assembly of a printer instrument. If the components are molded of plastic in order to reduce costs, tolerances become even more difficult to maintain. Furthermore, wedge type-tensioners 190 fail to compensate for the effect of varying spring 250 lengths and compression factors. Hence, a relatively wide range of belt tensions can result.